Adhesive tape

ABSTRACT

An adhesive tape comprising a base and, superimposed thereon, an adhesive layer, this adhesive layer comprising an adherent component (A), an epoxy resin (B), a thermally active latent epoxy resin curing agent (C), an energy radiation polymerizable compound (D) and a photopolymerization initiator (E), wherein either or both of the epoxy resin (B) and energy radiation polymerizable compound (D) have a dicyclopentadiene skeleton in its molecule or molecules thereof. The resultant adhesive tape has an adhesive layer which provides reduced water absorption of an adhesive curing product and which enables a lowering of the elastic modulus thereof during thermocompression bonding.

FIELD OF THE INVENTION

The present invention relates to a novel pressure sensitive adhesivetape. More particularly, the present invention relates to a pressuresensitive adhesive tape which is especially suitable for use in theprocess of dicing a silicon wafer or the like and performing die bondingof chips obtained by the dicing to a lead frame.

BACKGROUND OF THE INVENTION

A semiconductor wafer of, for example, silicon or gallium arsenide isproduced in the form of a large diameter. This wafer is cut andseparated (diced) into small element chips (IC chips) and is transferredto the subsequent mounting step. In this process, in particular, thesemiconductor wafer in the state of being stuck to a pressure sensitiveadhesive tape is subjected to dicing, cleaning, drying, expanding andpickup steps, and is transferred to the subsequent bonding step.

It is desired that the above pressure sensitive adhesive tape employedfrom the semiconductor wafer dicing step through the pickup step have anadhesive strength which is so large as to securely hold the wafer chipsin the dicing to drying steps but which is on such a level that noadhesive adheres to the wafer chips in the pickup step.

The chips having been picked up are bonded to lead frames with the useof a die bonding adhesive, such as an epoxy adhesive, in the die bondingstep. Thus, semiconductor devices are produced. However, when IC chipsare extremely small, application of an appropriate amount of adhesive isdifficult, and there has occurred such a problem that the adhesiveoverflows IC chips. On the other hand, when IC chips are large, therehas occurred such a problem that the bonding with satisfactory strengthcannot be attained because of, for example, an insufficient amount ofadhesive. Further, the application of such a die bonding adhesive islaborious. Therefore, there is a demand for an improvement enablingsimplification of the process.

For solving the above problems, various pressure sensitive adhesivetapes for wafer sticking which can perform both a wafer fixing functionand a die bonding function have been proposed (see, for example,Japanese Patent Laid-open Publication No. 2 (1990)-32181).

Japanese Patent Laid-open Publication No. 2 (1990)-32181 discloses apressure sensitive adhesive tape comprising a base and, superimposedthereon, an adhesive layer constituted of a composition which iscomposed of a (meth) acrylic acid ester copolymer, a general-purposeepoxy resin, a general-purpose photopolymerizable low-molecularcompound, a thermally active latent epoxy resin curing agent and aphotopolymerization initiator. This adhesive layer performs a waferfixing function at the time of wafer dicing. After the completion ofdicing, when exposed to energy radiation, the adhesive layer is curedwith the result that the adhesive strength between the adhesive layerand the base is lowered. Thus, upon picking up of IC chips, the pressuresensitive adhesive layer is detached together with the IC chips from thebase. The IC chips with the pressure sensitive adhesive layer aremounted on lead frames and heated. Consequently, the epoxy resincontained in the adhesive layer exerts a bonding strength to therebyfinalize bonding of the IC chips to lead frames.

The adhesive tape for wafer sticking disclosed in the above publicationenables so-called direct die bonding and enables omitting the step ofapplying a die bonding adhesive. That is, in the adhesive layer of theadhesive tape, all the components are cured upon the die bonding carriedout through the energy radiation curing and thermal curing, so that thechips and lead frames are bonded to each other with extremely largestrength.

Thereafter, generally, wire bonding is conducted via the reflow step.

For use in the reflow step, in recent years, solders not containing leadhave been developed in order to cope with environmental problems. Themelting temperature of the solders not containing lead is higher thanthat of conventional solder containing lead, thereby rendering highreflow temperatures inevitable. However, when the reflow temperature ishigh, even a small amount of water contained in the adhesive layer wouldvaporize and inflate, thereby causing the danger of package cracking.

Moreover, at the time of die bonding, it is demanded that the adhesivelayer properly follow the contour of adherend surface. In particular,for enhancing the follow property at the time of thermocompressionbonding, it is demanded that the elastic modulus of the adhesive layerbe low at the time of thermocompression bonding at high temperatures.However, the above conventional adhesives are unsatisfactory in thisrespect. Therefore, there is still a demand for improvement on pressuresensitive adhesives.

The present invention has been made in view of the above state of theprior art. It is an object of the present invention to provide anadhesive tape having an adhesive layer which enables reducing the waterabsorption of adhesive curing product and which enables lowering theelastic modulus thereof at thermocompression bonding.

SUMMARY OF THE INVENTION

The adhesive tape of the present invention comprises a base and,superimposed thereon, an adhesive layer, this adhesive layer comprisingan adherent component (A), an epoxy resin (B), a thermally active latentepoxy resin curing agent (C), an energy radiation polymerizable compound(D) and a photopolymerization initiator (E),

wherein either or both of the epoxy resin (B) and energy radiationpolymerizable compound (D) have a dicyclopentadiene skeleton in itsmolecule or molecules thereof.

In the present invention, it is preferred that the epoxy resin (B) havea dicyclopentadiene skeleton and be represented by the formula:

wherein n is an integer of 0 to 10.

It is also preferred that the energy radiation polymerizable compound(D) have a dicyclopentadiene skeleton and be represented by the formula:

wherein R is a hydrogen atom or a methyl group.

By the present invention, there is provided an adhesive tape having anadhesive layer which enables reducing the water absorption of adhesivecuring product to thereby avoid package cracking at the time of reflowand which enables lowering the elastic modulus thereof atthermocompression bonding to thereby ensure high capability of followingthe contour of adherend surface.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the adhesive tape of the present invention comprisesa base and, superimposed thereon, an adhesive layer, this adhesive layercomprising an adherent component (A), an epoxy resin (B), a thermallyactive latent epoxy resin curing agent (C), an energy radiationpolymerizable compound (D) and a photopolymerization initiator (E),

wherein either or both of the epoxy resin (B) and energy radiationpolymerizable compound (D) have a dicyclopentadiene skeleton in itsmolecule or molecules thereof.

First, each of the components constituting the adhesive layer will bedescribed in detail below.

Although acrylic, polyester, urethane, silicone and natural rubberpressure sensitive adhesives and other various general-purpose pressuresensitive adhesives can be used as the adherent component (A), it isespecially preferred in the present invention to employ acrylic pressuresensitive adhesives.

As the acrylic pressure sensitive adhesives, there can be mentioned, forexample, a (meth)acrylic ester copolymer composed of structural unitsderived from a (meth)acrylic ester monomer and a (meth)acrylic acidderivative. As the (meth)acrylic ester monomer, use can be made of anyof a (meth)acrylic acid cycloalkyl ester, benzyl (meth)acrylate and a(meth)acrylic acid alkyl ester having an alkyl group of 1 to 18 carbonatoms. Of these, it is especially preferred to use a (meth)acrylic acidalkyl ester having an alkyl group of 1 to 18 carbon atoms, such asmethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, propyl acrylate, propyl methacrylate, butyl acrylate orbutyl methacrylate. As the (meth)acrylic acid derivative, there can bementioned, for example, glycidyl (meth)acrylate having a glycidyl groupor hydroxyethyl acrylate having a hydroxyl group.

The content of structural units derived from glycidyl (meth)acrylate inthe (meth)acrylic ester copolymer is generally in the range of 0 to 80mol %, preferably 5 to 50 mol %. Introduction of a glycidyl group in the(meth)acrylic ester copolymer enhances the compatibility of the(meth)acrylic ester copolymer with the epoxy resin (B), increases the Tgof curing product and realizes an improvement of thermal stability.Introduction of a hydroxylated monomer, such as hydroxyethyl acrylate,in the (meth)acrylic ester copolymer facilitates controlling of theadherence to adherends and pressure sensitive adhesive properties.

The molecular weight of acrylic pressure sensitive adhesives ispreferably 100,000 or greater, still preferably in the range of 150,000to 1,000,000. The glass transition temperature of acrylic pressuresensitive adhesives is generally 20° C. or below, preferably in therange of about −70 to 0° C. The acrylic pressure sensitive adhesiveshave stickiness at room temperature (23° C.).

Epoxy resins having a dicyclopentadiene skeleton, used as the epoxyresin (B), each have a dicyclopentadiene skeleton and a reactive epoxygroup in the molecules thereof. The epoxy resins are generally solid atroom temperature, and the softening temperature thereof is preferably inthe range of about 40 to 90° C., still preferably 45 to 80° C., andoptimally 50 to 70° C. The molecular weight of such epoxy resins havinga dicyclopentadiene skeleton is preferably in the range of 430 to 3000,still preferably 700 to 2500, and optimally 1000 to 2000. The epoxyequivalent of epoxy resins having a dicyclopentadiene skeleton ispreferably in the range of 150 to 1000 g/eq, still preferably 200 to 800g/eq, and optimally 210 to 400 g/eq.

Among these epoxy resins (B) having a dicyclopentadiene skeleton, it isespecially preferred to employ an epoxy resin of the formula:

wherein n is an integer of 0 to 10. This n is preferably an integer of 0to 7, still preferably 0 to 5.

Mixtures of epoxy resins whose n values are different from each otherwithin the range of 0 to 10 are available as the epoxy resin having adicyclopentadiene skeleton. For example, as such epoxy resin mixtures,there can be mentioned epoxy resins XD-1000-L and XD-1000-2L(tradenames, produced by Nippon Kayaku Co., Ltd.).

These epoxy resins having a dicyclopentadiene skeleton may be usedindividually or in combination.

When, as the epoxy resin (B), an epoxy resin having a dicyclopentadieneskeleton is used without combination with other general-purpose epoxyresins described later, the epoxy resin is preferably added in an amountof 5 to 1000 parts by weight, still preferably 50 to 800 parts byweight, and optimally 100 to 600 parts by weight, per 100 parts byweight of the above adherent component (A).

Further, as the epoxy resin (B), the epoxy resin having adicyclopentadiene skeleton may be used in combination with othergeneral-purpose epoxy resins. As the general-purpose epoxy resins, it ispreferred to use an epoxy resin having a molecular weight of about 300to 2000. It is especially preferred to use a blend of an ordinarilyliquid epoxy resin of 300 to 500 molecular weight and an ordinarilysolid epoxy resin of 400 to 2000 molecular weight. The epoxy equivalentof such general-purpose epoxy resins is generally in the range of 50 to5000 g/eq. As such general-purpose epoxy resins, there can be mentioned,for example, glycidyl ethers of phenols such as bisphenol A, bisphenolF, resorcinol, phenylnovolak and cresol novolak; glycidyl ethers ofalcohols such as butanediol, polyethylene glycol and polypropyleneglycol; glycidyl ethers of carboxylic acids such as phthalic acid,isophthalic acid and tetrahydrophthalic acid; glycidyl or alkylglycidylepoxy resins obtained by substituting an active hydrogen bonded to anitrogen atom of aniline isocyanurate or the like with a glycidyl group;and so-called alicyclic epoxides obtained by, for example, oxidizing anintramolecular carbon to carbon double bond to thereby incorporate anepoxy group therein, such as vinylcyclohexane diepoxide,3,4-epoxycyclohexylmethyl-3,4-dicyclohexanecarboxylate and2-(3,4-epoxy)cyclohexyl-5,5-spiro(3,4-epoxy)cyclohexane-m-dioxane.

Of these, bisphenol glycidyl epoxy resins are preferably used as thegeneral-purpose epoxy resins. These general-purpose epoxy resins can beused individually or in combination.

In the present invention, at least either of the energy radiationpolymerizable compound (D) described later and the epoxy resin (B) musthave a dicyclopentadiene skeleton in the molecule thereof.

When, as the epoxy resin (B), epoxy resin having a dicyclopentadieneskeleton is not used and other general-purpose epoxy resins (not havinga dicyclopentadiene skeleton) are employed (when use is made of energyradiation polymerizable compound (D) having a dicyclopentadieneskeleton), the other general-purpose epoxy resins are preferably addedin an amount of 5 to 1000 parts by weight, still preferably 50 to 800parts by weight, and optimally 100 to 600 parts by weight, per 100 partsby weight of the above adherent component (A).

When the epoxy resin having a dicyclopentadiene skeleton is used incombination with other general-purpose epoxy resins, the sum of addedepoxy resins (B) is preferably in the range of 5 to 1000 parts byweight, still preferably 50 to 800 parts by weight, and optimally 100 to600 parts by weight, per 100 parts by weight of the above adherentcomponent (A). In this combination, the proportion of epoxy resin havinga dicyclopentadiene skeleton to other general-purpose epoxy resins ispreferably in the range of 1:99 to 99:1, still preferably 5:95 to 50:50,and optimally 10:90 to 40:60.

The thermally active latent epoxy resin curing agent (C) is a curingagent of such a type that it does not react with the epoxy resin (B) atroom temperature but, when heated to a certain temperature or above, isactivated to thereby react with the epoxy resin (B).

The activation of the thermally active latent epoxy resin curing agent(C) can be accomplished by various methods, for example, the methodwherein active species (anion and cation) are formed by chemicalreaction induced by heating; the method wherein the thermally activelatent epoxy resin curing agent (C) is stably dispersed in the epoxyresin (B) at about room temperature but, at high temperatures, isdissolved in the epoxy resin (B) to thereby initiate a curing reaction;the method wherein the curing agent is enclosed in a molecular sieve andis leached at high temperatures to thereby initiate a curing reaction;and the method wherein use is made of microcapsules.

The thermally active latent epoxy resin curing agents (C) can be usedindividually or in combination. In particular, dicyandiamide, imidazolecompounds and mixtures thereof are preferably used as the thermallyactive latent epoxy resin curing agent (C).

The thermally active latent epoxy resin curing agent (C) is generallyused in an amount of 0.1 to 20 parts by weight, preferably 0.5 to 15parts by weight, and optimally 1 to 10 parts by weight, per 100 parts byweight of the sum of epoxy resin having a dicyclopentadiene skeleton andother general-purpose epoxy resins.

The energy radiation polymerizable compound having a dicyclopentadieneskeleton, used as the energy radiation polymerizable compound (D), has adicyclopentadiene skeleton and one or more, preferably 2 to 10, energyradiation polymerizable groups in the molecule thereof. The molecularweight of the energy radiation polymerizable compound (D) is generallyin the range of about 150 to 840, preferably 250 to 500.

As the energy radiation polymerizable compound having adicyclopentadiene skeleton, preferred use is made of a polymerizablecompound of the formula:

wherein R is a hydrogen atom or a methyl group, preferably a hydrogenatom.

As the energy radiation polymerizable compound (D) having adicyclopentadiene skeleton, there can be mentioned, for example, R-684(trade name, produced by Nippon Kayaku Co., Ltd.).

The energy radiation polymerizable compounds (D) each having adicyclopentadiene skeleton maybe used individually or in combination.

When, as the energy radiation polymerizable compound (D), an energyradiation polymerizable compound having a dicyclopentadiene skeleton isused without the use of other general-purpose energy radiationpolymerizable compounds described later, the energy radiationpolymerizable compound (D) is preferably added in an amount of 0.1 to500 parts by weight, still preferably 10 to 200 parts by weight, andoptimally 20 to 100 parts by weight, per 100 parts by weight of theabove adherent component (A).

Further, as the energy radiation polymerizable compound (D), the energyradiation polymerizable compound having a dicyclopentadiene skeleton maybe used in combination with other general-purpose energy radiationpolymerizable compounds. The general-purpose energy radiationpolymerizable compounds each have at least one polymerizable double bondin the molecule thereof. The molecular weight thereof is generally inthe range of about 100 to 30,000, preferably 300 to 10,000. For example,low-molecular-weight compounds as disclosed in Japanese Patent Laid-openPublication Nos. 60(1985)-196956 and 60(1985)-223139 are widely used asthe above general-purpose energy radiation polymerizable compounds.Examples thereof include acrylate compounds, such as trimethylolpropanetriacrylate, tetramethylolmethane tetraacrylate, pentaerythritoltriacrylate, dipentaerythritol monohydroxypentaacrylate,dipentaerythritol hexaacrylate, 1,4-butylene glycol diacrylate,1,6-hexanediol diacrylate and polyethylene glycol diacrylate.

Furthermore, use can be made of oligomer acrylate compounds having afunctional group such as hydroxyl or carboxyl, for example, anoligoester acrylate, a urethane acrylate oligomer, an epoxy modifiedacrylate, a polyester acrylate, a polyether acrylate and an itaconicacid oligomer.

When, as the energy radiation polymerizable compound (D), energyradiation polymerizable compound having a dicyclopentadiene skeleton isnot used and only other general-purpose energy radiation polymerizablecompounds (not having a dicyclopentadiene skeleton) are employed (whenuse is made of epoxy resin (B) having a dicyclopentadiene skeleton), theother general-purpose energy radiation polymerizable compounds arepreferably added in an amount of 0.1 to 500 parts by weight, stillpreferably 10 to 200 parts by weight, and optimally 20 to 100 parts byweight, per 100 parts by weight of the above adherent component (A).

When the energy radiation polymerizable compound having adicyclopentadiene skeleton is used in combination with othergeneral-purpose energy radiation polymerizable compounds, the sum ofadded energy radiation polymerizable compounds (D) is preferably in therange of 0.1 to 500 parts by weight, still preferably 10 to 200 parts byweight, and optimally 20 to 100 parts by weight, per 100 parts by weightof the above adherent component (A). In this combination, the proportionof energy radiation polymerizable compound having a dicyclopentadieneskeleton to other general-purpose energy radiation polymerizablecompounds is preferably in the range of 1:99 to 99:1, still preferably20:80 to 70:30, and optimally 40:60 to 50:50.

The adhesive comprising the above energy radiation polymerizablecompound having a dicyclopentadiene skeleton and/or othergeneral-purpose energy radiation polymerizable compounds is cured uponbeing irradiated with light. As the light, use is made of, for example,ultraviolet light.

Mixing of the photopolymerization initiator (E) into the above adhesiveenables reducing not only the time of polymerization and curing but alsothe irradiation dose.

The photopolymerization initiator (E) can be selected from among, forexample, benzophenone, acetophenone, benzoin, benzoin methyl ether,benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether,benzoinbenzoic acid, methyl benzoinbenzoate, benzoindimethylketal,2,4-diethylthioxanthone, hydroxycyclohexyl phenyl ketone, benzyldiphenyl sulfide, tetramethylthiuram monosulfide,azobisisobutyronitrile, benzil, dibenzyl, diacetyl andβ-chloroanthraquinone.

The above photopolymerization initiator (E) is generally added in anamount of 0.5 to 15 parts by weight, preferably 1.0 to 10 parts byweight, and still preferably 1.5 to 6 parts by weight, per 100 parts byweight of the sum of energy radiation polymerizable compound having adicyclopentadiene skeleton and other general-purpose energy radiationpolymerizable compounds.

The adhesive layer of the adhesive tape of the present invention iscomposed of the above adherent component (A), epoxy resin (B), thermallyactive latent epoxy resin curing agent (C), energy radiationpolymerizable compound (D) and photopolymerization initiator (E) asessential components.

The adhesive layer composed of the above components has the propertiesof being curable by energy radiation and also curable by heating. Thus,the adhesive tape can be used as an adhesive for wafer fixing at thetime of dicing and can be used as an adhesive for thermocompressionbonding of chips to lead frames at the time of mounting. Although thisthermocompression bonding is generally performed by heating at 80 to150° C., the adhesive layer of the present invention exhibits a lowelastic modulus at this temperature range with the result that theadhesive tape can properly follow the contour of adherend surface tothereby enable attaining a secure bonding of chips to lead frames.

Finally, a curing product of high impact resistance can be provided bythermal curing. Further, the curing product has an excellent balance ofshear strength and peel strength, and can retain satisfactory bondingproperties even if exposed to severe thermal and humid conditions. Stillfurther, the water absorption of the curing product of adhesive layer isso low that the occurrence of package cracking at the reflow step can bereduced.

For the purpose of imparting electrically conductive properties afterdie bonding, the pressure sensitive adhesive layer may be loaded with anelectrically conductive filler such as gold, silver, copper, nickel,aluminum, stainless steel, carbon, ceramic or a material obtained bycoating nickel, aluminum or the like with silver. Further, for impartingthermally conductive properties, the pressure sensitive adhesive layermay be loaded with a thermally conductive filler such as gold, silver,copper, nickel, aluminum, stainless steel, silicon, germanium or othermetallic material or an alloy thereof. These additives may be added inan amount of about 10 to 400 parts by weight per 100 parts by weight ofthe adhesive component (namely, components A+B+C+D+E).

This adhesive layer can be loaded with an organic polyisocyanatecompound, an organic polyimine compound and the like in order toregulate the initial adhesive strength and cohesive strength thereofbefore exposure to energy radiation.

The organic polyisocyanate compound can be, for example, selected fromamong aromatic polyisocyanate compounds, aliphatic polyisocyanatecompounds, alicyclic polyisocyanate compounds, trimers of thesepolyisocyanate compounds and isocyanate-terminated urethane prepolymersobtained by reacting these polyisocyanate compounds with polyolcompounds. Specific examples of the organic polyisocyanate compoundsinclude 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate,diphenylmethane-4,4′-diisocyanate, diphenylmethane-2,4′-diisocyanate,3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate,dicyclohexylmethane-2,4′-diisocyanate and lysine isocyanate.

Specific examples of the above organic polyimine compounds include

-   N,N′-diphenylmethane-4,4′-bis(1-aziridinecarboxyamide),-   trimethylolpropane-tri-β-aziridinyl propionate,-   tetramethylolmethane-tri-β-aziridinyl propionate and-   N,N′-toluene-2,4-bis(1-aziridinecarboxyamido)triethylenemelamine.

It is generally preferred that these organic polyisocyanate compounds ororganic polyimine compounds be added in an amount of 0 to 10 parts byweight, especially 0.1 to 5 parts by weight, and still especially 0.5 to2 parts by weight, per 100 parts by weight of the adherent component(A).

Furthermore, an antistatic agent can be added to the above adhesivelayer. The addition of the antistatic agent can suppress the generationof static electricity at the expanding or pickup step, so that the chipreliability is enhanced. Examples of suitable antistatic agents includegenerally known activators such as anionic, cationic, nonionic andamphoteric activators. It is preferred that the antistatic agent be usedin an amount ranging from 0 to 50% by weight, especially from 0 to 30%by weight, based on the weight of the adhesive layer.

For example, when ultraviolet light is employed as the energy radiation,a transparent film is used as the base of the adhesive tape of thepresent invention. Examples of suitable transparent films include apolyethylene film, a polypropylene film, a polybutene film, apolybutadiene film, a polymethylpentene film, a polyvinyl chloride film,a vinyl chloride copolymer film, a polyethylene terephthalate film, apolyethylene naphthalate film, a polybutylene terephthalate film, apolyurethane film, an ethylene/vinyl acetate film, an ionomer resinfilm, an ethylene/(meth)acrylic acid copolymer film, anethylene/(meth)acrylic acid ester copolymer film, a polystyrene film anda polycarbonate film. Further, use is made of crosslinked filmstherefrom. Still further, laminate films therefrom may be used. On theother hand, when electron beams are employed as the energy radiation, itis not requisite for the base to be transparent. Therefore, use can bemade of not only the above transparent films but also opaque filmsobtained by coloring them, fluororesin films and the like.

The surface tension of the base is preferably 40 dyne/cm or less, stillpreferably 37 dyne/cm or less, and optimally 35 dyne/cm or less. Thisenables easily transferring of the adhesive layer of the adhesive tapeof the present invention to silicon chips at the time of die bonding.The above base with low surface tension can be obtained by selecting anappropriate material. Also, it can be obtained by subjecting the surfaceof the base to release treatment such as application of a silicone resinor the like.

The thickness of the base is generally in the range of about 10 to 300μm, preferably 20 to 200 μm, and still preferably 50 to 150 μm.

The adhesive tape of the present invention can be obtained by coatingthe base with the adhesive composition composed of the above componentsby customary means such as a roll knife coater, a gravure coater, a diecoater or a reverse coater, and drying the coating layer to thereby forman adhesive layer. According to necessity, the adhesive composition canbe dissolved or dispersed in a solvent before the coating operation.

It is generally preferred that the thickness of the thus formed adhesivelayer be in the range of 3 to 100 μm, especially 10 to 60 μm. The thusobtained adhesive tape is utilized in the following manner.

The adhesive tape of the present invention is stuck to one major surfaceof a silicon wafer, and the silicon wafer is fixed through the adhesivetape onto a dicing unit. The silicon wafer with the adhesive tape is cutinto IC chips by the use of cutting means such as a dicing saw.

The resultant adhesive tape stuck to IC chips is exposed to energyradiation. As the energy radiation which can be employed in the presentinvention, there can be mentioned, for example, ultraviolet light(central wavelength=about 365 nm) or electron beams. When ultravioletlight is used as the energy radiation, generally, the irradiationintensity is set so as to fall within the range of 20 to 500 mW/cm²while the irradiation time is set so as to fall within the range of 0.1to 150 sec. Further, for example, in the irradiation with electron beamsas well, conditions can be set with reference to those employed in theabove irradiation with ultraviolet light. In addition, at the time ofexposure to energy radiation, auxiliary heating can be effected.

This exposure to energy radiation enables detaching from the base theadhesive layer held stuck to one major surface of IC chips. The exposureto energy radiation may be performed prior to the dicing operation.

The obtained IC chips having the adhesive layer stuck thereto aremounted on lead frames, and heated so that the epoxy resin (B) of theadhesive layer is cured. Thus, the IC chips and lead frames are bondedto each other. The heating temperature is generally in the range ofabout 80 to 300° C., preferably about 80 to 250° C., and stillpreferably about 80 to 170° C. The heating time is generally in therange of 1 to 120 min, preferably 5 to 60 min. As a result of thisheating, the thermally curable adhesive component is cured to therebyattain strong bonding of the IC chips and lead frames to each other.Moreover, the adhesive layer composed of the above specified componentsexhibits a low elastic modulus at the time of thermocompression bonding,so that the adhesive layer properly follows the contour of adherendsurface with the result that the adherend and IC chips can be bonded toeach other with satisfactory strength. In this connection, the elasticmodulus (at 150° C.) of the adhesive layer exhibited after the curing ofthe energy radiation polymerizable compound (D) contained in theadhesive layer is preferably in the range of 1.0×10¹ to 8.0×10³ Pa,still preferably 3.0×10¹ to 5.0×10³ Pa, and optimally 1.0×10² to 1.0×10³Pa.

Furthermore, the final curing product after the curing of the epoxyresin (B) exhibits an extremely low water absorption coefficient, sothat, even if exposed to high temperatures at the time of reflow, thefinal curing product is free from water evaporation to thereby enablereducing the occurrence of package cracking. Accordingly, the waterabsorption coefficient (measured after exposure to 85% RH atmosphere at85° C. for 168 hr) of the finally cured adhesive layer is preferably2.3% or below, still preferably 2.0% or below, and optimally 1.9% orbelow.

Apart from the above usage, the adhesive tape of the present inventioncan be used in the bonding of semiconductor compounds, glass, ceramics,metals, etc.

By virtue of the present invention described above, there is provided anadhesive tape furnished with an adhesive layer which finally forms anadhesive curing product of low water absorption to thereby enablepreventing package cracking at the time of reflow, and which realizeslowering of the elastic modulus at thermocompression bonding, therebybeing excellent in the capability of following the contour of adherendsurface.

EXAMPLE

The present invention will further be illustrated below with referenceto the following Examples which in no way limit the scope of theinvention.

In the following Examples and Comparative Example, the“waterabsorptioncoefficient”, “elasticmodulus” and “peel strength” weremeasured in the following manners.

“Water Absorption Coefficient”

Adhesive tape pieces were piled one upon another into a laminate of1.0±0.2 mm thickness, and cut into a size of 50 mm×50 mm. Both majorsurfaces of the laminate were irradiated with ultraviolet light andheated at 160° C. for 1 hr to thereby effect thermal curing. The thusobtained sample was allowed to stand still in an atmosphere of 85%relative humidity at 85° C. for 168 hr. The water absorption coefficientwas calculated from any weight increase of the sample.

“Elastic Modulus”

With respect to each of the adhesives of the Examples and ComparativeExample, one not containing any thermally active latent epoxy resincuring agent (C) was prepared. Both major surfaces of a sample thereofwere irradiated with 200 mJ/cm² ultraviolet light. With respect to theresultant sample, the elastic modulus at 150° C. according to thetorsion shear method was measured by the use of RDA II manufactured byRheometric Scientific F. E. Ltd. at 1 Hz.

“Peel Strength”

Each of the adhesive tapes was stuck to #2000 polished surface of a 350μm thick silicon wafer, irradiated with ultraviolet light of 230 mJ/cm²light quantity, and diced into a size of 10 mm×10 mm. Thereafter, eachsilicon chip with adhesive obtained by detaching the base from theadhesive layer was compression bonded to a 150 μm thick copper sheet of10 mm×50 mm at 150° C. for 1 sec, and allowed to stand still in athermostat chamber at 160° C. for 1 hr to thereby effect thermal curingof the adhesive layer. Thus, a sample for measuring peel strength wasobtained.

The silicon chip side of the sample was fixed by bonding, and the coppersheet was peeled at an angle of 90° to thereby effect measuring of thepeel strength (mN/10 mm). The peeling speed was 50 mm/min.

In the Examples and Comparative Example described below, the followingmaterials were used as the adherent component (A), epoxy resin (B),thermally active latent epoxy resin curing agent (C), energy radiationpolymerizable compound (D) and photopolymerization initiator (E).

(A) Adherent Component

copolymer of 900,000 weight average molecular weight and −28° C. glasstransition temperature, obtained by copolymerizing 55 parts by weight ofbutyl acrylate, 10 parts by weight of methyl methacrylate, 20 parts byweight of glycidyl methacrylate and 15 parts by weight of 2-hydroxyethylacrylate.

(B) Epoxy Resin

-   (B1): liquid bisphenol A epoxy resin (epoxy equivalent: 180 to 200,    softening point: nil, molecular weight: about 420)-   (B2): solid bisphenol A epoxy resin (epoxy equivalent: 800 to 900,    softening point: 93° C., molecular weight: about 1700)-   (B3) epoxy resin having a dicyclopentadiene skeleton (trade name    XD-1000-L produced by Nippon Kayaku Co., Ltd., epoxy equivalent: 240    to 250, softening point: 66° C., n=0.6 to 0.7)-   (B4) epoxy resin having a dicyclopentadiene skeleton (trade name    XD-1000-2L produced by Nippon Kayaku Co., Ltd., epoxy equivalent:    240 to 250, softening point: 57° C., n=0.3 to 0.4)-   (B5): solid o-cresol novolak epoxy resin (epoxy equivalent: 210 to    230, softening point: 92° C., molecular weight: about 1650).

(C) Thermally Active Latent Epoxy Resin Curing Agent (Epoxy Hardener)

-   (C1): dicyandiamide (trade name: Hardener 3636AS, produced by Asahi    Denka Kogyo K.K.)-   (C2): 2-phenyl-4,5-dihydroxymethylimidazole (trade name: Curezol    2PHZ, produced by Shikoku Chemicals Corporation)

(D) Energy Radiation Polymerizable Compound

-   (D1): energy radiation polymerizable compound having a    dicyclopentadiene skeleton (trade name: Kayarad R684, produced by    Nippon Kayaku Co., Ltd., molecular weight: 304)-   (D2): dipentaerythritol hexaacrylate (molecular weight: 578).

(E) Photopolymerization Initiator

1-hydroxycyclohexyl phenyl ketone.

(F) Other

-   crosslinking agent: aromatic polyisocyanate    (trimethylolpropane adduct of toluylene diisocyanate).

Example 1

An adhesive composition was obtained by mixing the components togetherin the proportions as specified in Table 1. A base of a 90 μm thicklaminate film composed of a plasticized PVC layer and a layer ofethylene/methacrylic acid copolymer on its side of ethylene/methacrylicacid copolymer layer (surface tension: 35 dyn/cm) was coated with thisadhesive composition so that a 20 μm adhesive layer was formed on thebase. Thus, an adhesive tape was obtained.

The “water absorption coefficient”, “elastic modulus” and “peelstrength” of the obtained adhesive tape were measured in the abovemanners. The results are listed in Table 1.

Examples 2 to 4 and Comparative Example 1

The same operations as in Example 1 were repeated except that theproportions of added components were changed as specified in Table 1.The results are listed in Table 1.

TABLE 1 Compsn. of adhesive layer (pts. wt.) energy radia- tion ad-poly- her- epoxy meri- photopo- cross- Water Elastic ent curing zablelymn, linking absorption modulus Peel compo- epoxy resin agent compd.initia- agent coefficient (150° C.) strength nent A B1 B2 B3 B4 B5 C1 C2D1 D2 tor (E) (F) (%) (Pa) (mN/10 mm) Example 1 20 20 40 20 1 1 10 0.30.3 1.89 5.21 × 10² 7000 Example 2 20 20 40 20 1 1 10 0.3 0.3 1.87 3.14× 10² 6500 Example 3 20 20 40 20 1 1 10 0.3 0.3 2.09 6.03 × 10² 7800Example 4 20 20 40 20 1 1 10 0.3 0.3 2.24 1.10 × 10³ 7500 Comp. Ex. 1 2020 40 20 1 1 10 0.3 0.3 2.59 8.85 × 10³ 8000

1. An adhesive tape comprising a base and, superimposed thereon, anadhesive layer, said adhesive layer comprising an adherent component(A), an epoxy resin (B), a thermally active latent epoxy resin curingagent (C), an energy radiation polymerizable compound (D) and aphotopolymerization initiator (E), wherein the epoxy resin (B) has adicyclopentadiene skeleton and is represented by the formula:

wherein n is an integer of 0 to
 10. 2. The adhesive tape as claimed inclaim 1, wherein the energy radiation polymerizable compound (D) has adicyclopentadiene skeleton and is represented by the formula:

wherein R is a hydrogen atom or a methyl group.